I have '6' mapped for the emu list. I press that, use the left digital stick to scroll to the desired emulator, then press '1' to select. Same process when I go back to MAME.
However, from MAME, right-clicking the mouse and selecting another emulator, and that again and selecting MAME gives the same result.
In essence, regardless of method, selecting MAME from any other emulator gives this result.